Electric Ni plating is one of surface treatment methods for forming an Ni plating layer on a substrate surface made of a conductive metal, and the Ni plating layer formed exhibits excellent corrosion resistance. Thus, plated articles which are electrically Ni-plated have been extensively used in electronic parts and the like for an automobiles or home electric appliances. In recent years, there have been needed plated articles having further improved electric, mechanic and chemical properties as automobiles and home electric appliances have become highly functional.
It is known that electric, mechanic or chemical properties of a plated article can be further improved by forming a porous Ni plating layer on a substrate surface. Furthermore, a plated article having a porous Ni plating layer can be used as an electric part such as a connector because it exhibits low contact electrical resistance and excellent corrosion resistance and slidability; can be used as an electrode such as an electrode for hydrogen generation because it is very porous and has a large surface area; and can be used as a heat sink because it exhibits good heat dissipation performance. Recently it is, therefore, regarded that technique for forming a porous Ni plating layer on a substrate surface is one of the particularly important techniques.
A method described in Patent Reference No. 1 can be mentioned as an example of a method for forming a porous Ni plating layer on a substrate surface. Patent Reference No. 1 has described a method for forming a porous Ni plating layer on a substrate surface, comprising immersing a substrate in a plating solution containing a quaternary ammonium salt (dodecyltrimethylammonium chloride) and electroplating the substrate. However, the method described in Patent Reference No. 1 requires the use of a plating solution containing a special salt, and is, therefore, not always a simple method.
Patent Reference No. 2 has disclosed that an Ni-plating surface can be roughened for improving adhesiveness to another film. Patent Reference No. 2 has described that a plating solution used for a nickel plating bath for forming a rough plating layer can contain 2.5 to 3.5 g/L of nickel sulfate or nickel chloride, 2.5 to 3.0 g/L of ammonium sulfate, 4.5 to 5.0 g/L of sodium sulfate, 1.5 to 2.0 g/L of sodium chloride, and 2.0 to 3.0 g/L of boric acid. It has also described that by applying a high current density of 10 ASD (A/dm2) or more, a nickel plating layer with large surface roughness can be formed. However, it cannot form a porous Ni plating layer, and thus only roughening the surface cannot improve electric and/or chemical properties of a plated article.
Non-patent Reference No. 1 has described a method for forming a porous Ni plating layer on a substrate surface. Specifically, Non-patent Reference No. 1 has described electric Ni plating using a plating solution containing 0.2 M Ni chloride and 2.0 M ammonium chloride at pH 3.61, where a cathode current density of more than 300 mA/cm2 (30 A/dm2) can form an Ni plating layer having cavities and pores over the whole surface. However, the method described in Non-patent Reference No. 1 cannot form a uniform porous Ni plating layer over the whole surface of a substrate, and it cannot be thus expected to fully improve electric, mechanic or chemical properties of a plated article to be produced.